1. Field of the Invention
The present invention relates to a photoelectric device for converting the light intensity incident thereon into a quantity of electricity corresponding to the intensity, and more particularly relates to a photoelectric device for use in a radiation thermometer which measures a temperature of a target without being in contact therewith.
2. Description of the Prior Art
A heretofore proposed radiation thermometer includes a photoelectric device for converting the light intensity into the quantity of electricity corresponding thereof. The photoelectric device contains a photoelectric element having a light receiving surface to convert the intensity of the light incident on the light receiving surface into the quantity of electricity corresponding thereof. The proposed radiation thermometer can measure the temperature of a target distant therefrom based on the converted quantity of electricity corresponding to the intensity of the light which has been radiated from the target and incident on the light receiving surface of the photoelectric element. Therefore, the radiation thermometer is used with the light receiving surface directed toward a target whose temperature should be measured.
However, a photoelectric element generally has a characteristic that the rate of the conversion from the light intensity into the quantity of electricity changes with the temperature of the element. Therefore, unless such are taken into consideration, error will occur in the measurement by a radiation thermometer. To avoid this error, the following methods have been proposed:
(1) One method is to compensate the quantity of electricity converted by the photoelectric element for the temperature thereof. It is necessary to previously measure the change of the conversion rate of the photoelectric element with the change of the temperature thereof, and to locate a temperature sensor such as a thermocouple or a thermistor close to the photoelectric element. According to this method, the quantity of electricity of the photoelectric element is compensated based on the characteristics thereof of previously measured and the temperature measured by the temperature sensor. PA0 (2) Another method is to keep the photoelectric element at a constant temperature. It is necessary to locate a temperature control device close to the photoelectric element in addition to the temperature sensor as described above. The temperature of the photoelectric element is kept at constant by the temperature control device which operates based on the temperature measured by the temperature sensor.
However, in both methods as described in (1) and (2), since it is necessary to locate a temperature sensor close to the photoelectric element, the photoelectric device including the temperature sensor can not be compact in size. The photoelectric device using the method (2) will be more cumbersome since it requires a temperature control device which must be located close to the photoelectric element in addition to the temperature sensor. Furthermore, since the temperature measured by the temperature sensor is not the temperature of the photoelectric element itself, the correct temperature compensation based on the temperature of the photoelectric element itself or the precise temperature control based on the temperature of the photoelectric element itself is impossible. Furthermore, since the speed of the temperature change of the photoelectric element is ordinary different from that of the temperature sensor, the correct and quick temperature measurement can not be achieved by the radiation thermomenter using the method (1) or (2).